Using co2, and have proper ventilation? I'm a little confused, please explain.600 is perfect for 3x3. The 2x 400s is overkill IMO unless you're using CO2 and have proper ventilation.
So your saying we should be exhausting while using co2 enrichment?Just your plants need a certain amount of CO2 to be able to use that much light effectively, and that much light also produces a lot of heat.